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GRAANGIDS
2016
GRAIN GUIDE
the potential for fires as a result of the large amount of biomass it produces; obstruction (vi-
sion); seeds cling to fruit, which reduces the quality of the fruit; leaves are very sharp – can injure
humans and animals; causes respiratory problems in humans (aggravate asthma); plant causes
skin irritations. Mechanical control of the plant is very difficult, as it will harm the surroundings.
Small plants can be pulled out by hand, but it is labour intensive. There are no biological control
agents for the plant. Various chemicals are registered for controlling pampas grass. According to
the CARA Act it is a category 1 plant – the landowner must therefore control it.
Salvinia molesta D.S.Mitch.
The kariba weed is indigenous to South America (Brazil) and
entered South Africa as an ornamental plant for fish ponds
and aquariums. From these sources it spread to other water
sources. Kariba weed is a free-floating water fern with hori-
zontal, branched rootstocks without roots. The kariba weed
propagates vegetatively, in other words each section of the
plant that breaks off has the potential to form a new plant. It
is because of this property that it can form very dense stands
extremely quickly. It can occur in any body of water – rivers,
dams, lakes, irrigation channels and drainage channels.
The negative aspects of the kariba weed include the fol-
lowing: It changes the appearance of the body of water;
competes for space, light and nutrients; smothers any other
plants that occur; obstruction (access with boats, for exam-
ple); obstruction of water flow; increases water loss consider-
ably; increases habitat for mosquitoes and bilharzia-bearing
snails considerably; reduces water quality considerably as it
removes oxygen from the water; increases deaths among natural aquatic animals.
Mechanical control of the plants is usually recommended – start with the smallest infestations first.
However, it is important for every part of all plants to be removed, as the smallest part can lead
to the development of new plants. Chemicals can also be used very well in combination with
mechanical control. However, as the plants occur in bodies of water, chemicals must be used with
care. There are also effective biological control agents for this plant – in Australia in particular
great success has been achieved with bio-agents. According to the CARA Act the kariba weed is a
category 1 plant – it must therefore be controlled.
Eichhornia crassipes (C.Mart.) Solms
Water hyacinths originally come from South America, particu-
larly from the Amazon. Water hyacinths are aquatic plants,
free floating or anchored in shallow water and can multiply
rapidly through runners that form new plants. The roots of
floating plants are long and penniform. In shallow water the
roots will penetrate the soil – only under these conditions will
the plant form flowers. Water hyacinths propagate vegetative-
ly or through seeds, which can survive up to 15 years. Water
hyacinths occur in eutrophic, nutrient-rich bodies of water like
dams, rivers and canals in particular. The negative aspects of
water hyacinths are the following: Compete for light, space
and nutrients; reduce the possibility of physical movement
through the water; change the habitat and landscape (reduce
the aesthetic value); reduce opportunities like fishing; can
cause mechanical damage to hydro-electric installations;
reduce the irrigation capacity of channels and rivers; reduce
Ten main invasive plants in South Africa
Continued from p. 85
Salvinia molesta
Eichhornia crassipes